In recent years, various proposals have been made in regard to automotive vehicle body structures to maximize the protection of vehicle occupants at the time of a vehicle crash. For instance, proposals have been made to minimize the deceleration of the part of the vehicle body occupied by vehicle occupants by properly selecting the deformation of the remaining part of the vehicle body, and preventing the former part of the vehicle body from deforming (see Japanese patent laid open publication No. 7-101354, for instance).
However, it may be difficult to reduce the deceleration of the vehicle occupant in the case of small cars which do not provide adequate deformation strokes of the parts of the vehicle body other than the part occupied by the vehicle occupant only with such conventional approaches which essentially consist of attempts to reduce the deceleration of the passenger compartment by controlling the deformation mode of the vehicle body.
Further, it is generally impossible to integrally hold a vehicle occupant to a vehicle body even if the seat is fixedly attached to the vehicle body because the seat belt for restraining the vehicle occupant to the seat has an inevitable slack. Thus, when a vehicle crash occurs, the forward inertia force acting upon the vehicle occupant at the time of a vehicle crash starts rising only after the vehicle occupant is fully restrained by the seat belt. Further, because the seat belt inevitably has a certain resiliency, the deceleration acting on the vehicle occupant, who tends to continue to move forward, reaches a maximum level only when the maximum elongation of the seat belt takes place. The maximum deceleration level increases as the forward movement of the vehicle occupant with respect to the vehicle body under the inertia force increases, and is known to substantially exceed the average deceleration of the vehicle body. Therefore, in order to minimize the impact which the vehicle occupant receives at the time of a vehicle crash, it is necessary to minimize the time delay in the rise in the deceleration of the vehicle occupant with respect to the deceleration of the vehicle body and thereby reduce the forward movement of the vehicle occupant with respect to the vehicle body.
Proposals have been made in copending U.S. patent application Ser. Nos. 09/377,366 and 09/376,888 both filed on Aug. 18, 1999, to impart a relative deceleration and acceleration to the vehicle seat or the member carrying the vehicle seat with respect to the main part of the vehicle body so that the vehicle occupant may experience a deceleration from an early stage of a vehicle crash, and the maximum vehicle occupant deceleration may be reduced by distributing the inertia force acting on the vehicle occupant over a longer period of time. There are additional copending U.S. patent applications of later filing dates which also relate to similar subject matters. The contents of these applications are hereby incorporated in this application by reference.